Rotary drill bits are frequently used to drill oil and gas wells, geothermal wells and water wells. Rotary drill bits may be generally classified as rotary cone or roller cone drill bits and fixed cutter drilling equipment or drag bits. Fixed cutter drill bits or drag bits are often formed with a bit body having cutting elements or inserts disposed at select locations of exterior portions of the bit body. Fluid flow passageways are typically formed in the bit body to allow communication of drilling fluids from associated surface drilling equipment through a drill string or drill pipe attached to the bit body.
Fixed cutter drill bits generally include a metal shank operable for engagement with a drill string or drill pipe. Various types of steel alloys may be used to form a metal shank. A bit head may be attached to an associated shank to form a resulting bit body.
For some applications a bit head may be formed from various types of steel alloys satisfactory for use in drilling a wellbore through a downhole formation. The resulting bit body may sometimes be described as a “steel bit body.” For other applications, a bit head may be formed by molding hard, refractory materials with a metal blank. A steel shank may be attached to the metal blank. The resulting bit body may be described as a “matrix bit body.” Fixed cutter drill bits or drag bits formed with matrix bit bodies may sometimes be referred to as “matrix drill bits.”
Matrix drill bits are often formed by placing loose infiltration material or matrix material (sometimes referred to as “matrix powder”) into a mold and infiltrating the matrix material with a binder such as a copper alloy. Other metallic alloys may also be used as a binder. Infiltration materials may include various refractory materials. A preformed metal blank or bit blank may also be placed in the mold to provide reinforcement for a resulting matrix bit head. The mold may be formed by milling a block of material such as graphite to define a mold cavity with features corresponding generally with desired exterior features of a resulting matrix drill bit.
Various features of a resulting matrix drill bit such as blades, cutter pockets, and/or fluid flow passageways may be provided by shaping the mold cavity and/or by positioning temporary displacement material within interior portions of the mold cavity. An associated metal shank may be attached to the bit blank after the matrix bit head has been removed from the mold. The metal shank may be used to attach of the resulting matrix drill bit with a drill string.
A wide variety of molds have been used to form matrix bit bodies and associated matrix drill bits. U.S. Pat. No. 5,373,907 entitled “Method And Apparatus For Manufacturing And Inspecting The Quality Of A Matrix Body Drill Bit” shows some details concerning conventional mold assemblies and matrix bit bodies.
A wide variety of molds and castings produced by such molds have been used to form steel bit bodies and associated fixed cutter drill bits.